As the world focuses on lowering carbon emissions to tackle climate change, heat pump systems have become a hot topic. So, you may be asking, what is a heat pump and how does it work?
In this comprehensive guide, we cover everything you need to know about heat pump systems: how they work, the different types available, heat pump installation cost, the advantages, and disadvantages to having one, and what you need to consider if you’re thinking about installing one.
What is a Heat Pump?
Air Source Heat Pump
A heat pump is a system that extracts heat energy from outside, then brings it inside to heat a home or other property. The pump itself is located outside and looks similar to an air-conditioning unit.
Heat pump systems are better for the environment because they are run entirely by electricity rather than carbon-emitting fossil fuels. And because they deliver more heat energy than the electrical energy they use, they are typically more efficient to run than gas or oil-based heating systems or electric heaters.
How Does a Heat Pump Work?
An air source heat pump works a bit like a fridge operating in reverse:
Inside the pump is a network of tubes filled with refrigerant that absorbs heat from the air
Inside the pump is a network of tubes filled with refrigerant that absorbs heat from the air
Using electricity, the heat pump then compresses the refrigerant to increase its pressure, raising its temperature and changing it from a liquid to a gas
This gas is then passed through a heat exchanger into the heating system inside the building
The heating system circulates the heat around the building through underfloor heating systems, radiators, and hot water tanks.
Types of Heat Pump
There are three types of heat pumps available:
Air source heat pumps
Ground source heat pumps
Water source heat pumps
They all work in a similar way, but their main difference is where they draw their heat from.
Let’s look at the three types.
Air Source Heat Pumps
All air source heat pumps work by extracting heat from the outside air and transferring it indoors. There are two ways the heat can be transferred: either through a water-based system or an air-based system.
Both systems can also be combined with a hybrid system – where the air source heat pump is used alongside a more traditional fossil fuel system such as a boiler.
Let’s look at the three systems:
- Air-to-water heat pumps
Air-to-water heat pumps are the most commonly used heat pumps in the UK because they are suitable for many homes. As the name suggests, they extract heat from the outside air and transfer it into a water-based heating system – namely radiators, underfloor heating, and hot water tanks. - Air-to-air heat pumps
Air-to-air heat pumps extract heat from the outside air, just like an air-to-water heat pump. Instead of transferring the heat energy into a water-based heating system, the energy is transferred into an air heating system through vents or wall heaters. This heat pump system is often used in small properties, such as flats, and is ideal for replacing old electric systems such as storage heaters.
An air-to-air heat pump doesn’t supply hot water, though. So, if one of these heat pumps is installed, a boiler or immersion heater for hot water will also be needed. - Hybrid air source heat pumps
All heat pumps are designed to deliver lower temperatures than traditional heating methods. That means radiators and hot water won’t get as hot as they would with a boiler, for example, and they take longer to heat up.
So, a hybrid heat pump can be combined with an existing central heating system or boiler to give the heating or hot water a quick boost when it’s needed.
Other Things You Need to Know
What Size Heat Pump Do You Need?
Heat pump size is measured in kilowatts. Air source heat pumps can range from 5kW up to 16kW or more. Generally, the bigger the property you’re heating, the bigger the heat pump you’ll need. However, it also depends on other factors, such as how well the home is insulated, how many rooms it has and how many radiators there are. Calculating the correct size should always be carried out by a qualified heat pump installer.
Types of home Types of home ASHP recommended output (kW) GSHP recommended output (kW)
1-2 bedroom small home 5 4
3 bedroom with poor insulation 9 8
4 bedroom with efficient insulation 9 8
4 bedroom with poor insulation 16 15
5 bedroom with efficient insulation 16 15
*Data in the above table is true to Screwfix’s knowledge at the time of writing.
How noisy are air source heat pump?
All air source heat pumps have an outdoor unit that contains a fan, so there will be some noise, and the volume will depend on the size of the pump and manufacturer. However, modern heat pumps shouldn’t make anything more than a low whirring sound.
How efficient are air source heat pumps?
Heat pump efficiency is measured as the Coefficient of Performance (CoP). This calculates the amount of inputted energy compared to the amount of outputted energy. So, if a heat pump uses 1kW of electricity to generate 4kW of heat, the CoP is 4. The higher the CoP, the more efficient the pump is. All air source heat pumps deliver more heat energy than the electrical energy they use, so they are typically very efficient to run.
Ground Source Heat Pump
Ground Source Heat Pump
Ground source heat pumps work by drawing heat energy from the ground through pipes filled with heat transference fluid and anti-freeze. The fluid circulates through the pipes then goes up into the heat pump located outside at ground level. The liquid is then heated and transferred into the home in the same way an air source heat pump works.
Ground source heat pumps are more efficient than air source heat pumps. However, due to the more extensive work needed to install them, they tend to cost more. The pipes can be buried either vertically (digging to a depth of 150m) or horizontally (to heat an average-sized home, you’ll need an outside area that’s roughly the size of a tennis court, and the pipes would be buried at around 1m deep).
For this reason, ground source heat pumps are better suited to new build homes so their installation can be planned into the construction process.
Water Source Heat Pump
Water Source Heat Pump
Water source heat pumps work in a similar way to ground source heat pumps, but instead of drawing heat from pipes buried in the ground, the pipes are placed in a body of water. And instead of having a heat pump on the outside of the property, it’s placed inside.
For this reason, a home will need enough room inside for the heat pump to be installed, and ideally, it will need to be in a room where its low hum isn’t going to annoy anyone.
Water source heat pumps are often more efficient than air and ground source heat pumps because heat transfers better in water, and water temperatures tend to stay fairly stable throughout the year.
However, the property needs to be very close to a large water source, such as a river or lake, and you need to be able to lay pipes between the water source and the property on land that’s within the property’s boundary.
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